The present invention relates to prosthetic heart valves, and, more particularly, to a prosthetic tissue valve having increased flexibility enabling it to follow the motions of the annulus and sinus regions.
Prosthetic heart valves are used to replace damaged or diseased heart valves. In vertebrate animals, the heart is a hollow muscular organ having four pumping chambers: the left and right atria and the left and right ventricles, each provided with its own one-way outflow valve. The natural heart valves are identified as the aortic, mitral (or bicuspid), tricuspid and pulmonary valves. The valves of the heart separate chambers therein, and are each mounted in an annulus therebetween. The annuluses comprise dense fibrous rings attached either directly or indirectly to the atrial and ventricular muscle fibers. Prosthetic heart valves can be used to replace any of these naturally occurring valves, although repair or replacement of the aortic or mitral valves are most common because they reside in the left side of the heart where pressures are the greatest. In a valve replacement operation, the damaged leaflets are excised and the annulus sculpted to receive a replacement valve.
The four valves separate each ventricle from its associated atrium, or from the ascending aorta (left ventricle) or pulmonary artery (right ventricle). After the valve excision, the annulus generally comprises a ledge extending into and defining the orifice between the respective chambers. Prosthetic valves may attach on the upstream or downstream sides of the annulus ledge, but outside of the ventricles to avoid interfering with the large contractions therein. Thus, for example, in the left ventricle a prosthetic valve is positioned on the inflow side of the mitral valve annulus (in the left atrium), or on the outflow side of the aortic valve annulus (in the ascending aorta).
Two primary types of heart valve replacements or prostheses are known. One is a mechanical-type heart valve that uses a ball and cage arrangement or a pivoting mechanical closure to provide unidirectional blood flow. The other is a tissue-type or xe2x80x9cbioprostheticxe2x80x9d valve which is constructed with natural-tissue valve leaflets which function much like a natural human heart valve, imitating the natural action of the flexible heart valve leaflets which seal against each other to ensure the one-way blood flow.
Prosthetic tissue valves comprise a stent having a rigid, annular ring portion and a plurality of upstanding commissures to which an intact xenograft valve or separate leaflets of, for example, bovine pericardium are attached. The entire stent structure is typically cloth-covered and a sewing ring is provided around the periphery for attaching to the natural annulus. Because of the rigidity of the material used in the stent and/or wireform, conventional valves have a diameter that is minimally affected by the natural motion of the heart orifice. In the aortic position, the commissures extend in the downstream direction a spaced distance from the walls of the downstream aortic wall. Movement of the aortic wall or sinuses does not directly affect movement of the cantilevered commissures, though fluid flow and pressures generated by movement of the walls ultimately does cause the commissures to dynamically flex to some extent (i.e., they are cantilevered downstream in the aorta). Because of the inherent rigidity in conventional heart valves, the natural dilatation of the annulus is restricted, imposing an artificial narrowing of the orifice, and increasing the pressure drop therethrough.
Accordingly, there is a need for a more flexible heart valve that responds to the natural motions of the annulus and downstream vessel walls.
The present invention allows the prosthesis to follow the aortic wall motion as well as that of the annulus during systole and diastole phases, thus reducing the loss in pressure caused by restriction of such motions. The solution is a heart valve having a plurality of leaflets, preferably three, directly sutured to the aortic wall, replacing the native valve.
The present invention provides a heart valve including a flexible wireform or stent that allows relative cusp movement or pivoting. The continuous maintenance of leaflet orientation at the commissures provides durability and predictability. Though the leaflets are not wholly independent, they are allowed to move in regions of greatest anatomical motion.
The present invention differs in another respect from bioprosthetic tissue valves of the prior art because it does not include a conventional sewing ring with attendant rigid stent. Alternating peripheral cusps and commissures of the prosthetic valve are attached to the annulus region and the sinus region of the ascending aorta of the host (in the aortic valve version), downstream from the location of the natural leaflets (typically excised).
In accordance with one aspect of the present invention, a prosthetic heart valve is provided including a flexible, generally cylindrical stent having alternating cusps and commissures. A plurality of flexible leaflets is attached to the stent so as to form a one-way valve within the cylinder. A flexible band is attached along the stent and has a free edge extending away from the stent along the alternating cusps and commissures for connecting the heart valve to an anatomical orifice.
Another aspect of the present invention is a highly flexible heart valve including a stent/leaflet subassembly having a peripheral stent and a plurality of leaflets disposed therewithin. The stent/leaflet subassembly defines alternating cusps and the commissures. A connecting band is attached to the stent/leaflet subassembly and follows the alternating cusps and commissures. The band includes a free edge extending from the stent for connecting the heart valve to an anatomical orifice.
In a still further aspect of present invention, a prosthetic heart valve comprises a plurality of flexible leaflets, each having an arcuate cusp edge and a coapting edge. The heart valve includes a stent with a plurality of cusps connected to each other at upstanding commissures to generally define a substantially cylindrical volume therebetween. The leaflets are attached to the stent within the cylindrical volume and the cusps are free to move with respect to one another about the commissures.
In another embodiment, the present invention provides a prosthetic heart valve comprising a stent having a plurality of stent members adjacently disposed generally around a circle to define a substantially cylindrical volume therebetween. The stent includes a plurality of alternating cusps and commissures. Preferably, the stent members each have a cusp and two commissure regions, with adjacent commissure regions of the stent members together defining each of the commissures of the stent. The stent members may be coupled together to pivot or flexibly move with respect to one another. The coupling may be permanent, or may comprise a bio-resorbable structure that permits the stent members and associated leaflets to move independently from one another.
A further aspect of the invention is a heart valve having three leaflets which are directly sutured to the aortic wall, replacing the native valve. In one embodiment, the commissures of adjacent cusps may be connected during implant, and can become independent thereafter. This gives the cusps and commissures freedom to move during systole and diastole, thus improving the pressure gradient. To facilitate implantation, the commissures may be initially temporarily connected, such as with a biodegradable material. In a minimally invasive contexts, the valve may be partially collapsible to facilitate delivery through a narrow channel to the implantation site.
Alternatively, the invention provides a reduced pressure gradient prosthetic heart valve that has multiple, preferably three, totally or partially independent leaflets. The leaflets are directly sutured to the aortic wall, replacing the native valve. The commissures of adjacent leaflets may be connected during implant and become independent thereafter, or they may be linked together at the commissure. For example, adjacent commissures may be linked by fasteners that are either unique to each leaflet (a commissure clip or a clip in conjunction with a cusp support), or comprise a continuous scalloped wire or frame around all of the leaflets. The fastener must be sufficiently flexible to preserve the motion of the three leaflets during systole. Because of the independent (or flexibly coupled) nature of the leaflets, the commissures are free to move during the systole/diastole cycle, and the pressure gradient through the valve is therefore significantly reduced.
Still further, the invention contemplates the replacement of a single leaflet with an independent prosthetic leaflet, while the other native leaflets remain and are still functional. That is, if one native leaflet is not functioning because of disease or other condition, the entire valve need not be replaced, just the damaged leaflet. The present invention thus enables a less invasive procedure that obviates the removal of healthy leaflets. Still further, a minimally-invasive implantation device may be used to deliver and implant the independent leaflet(s).
Desirably, the stent of the prosthetic heart valve of the present invention is configured to permit the cusps and commissures to move radially in and out. In one embodiment, the stent comprises a cloth covered rod-like structure. The cloth covering closely surrounds the stent and includes a flap projecting therefrom substantially the entire length of the cusps and commissures for connecting the stent to both the flexible band and the leaflets. The band preferably comprises a suture-permeable inner member, such as silicone, covered by cloth. The cusps of the stent may be pivotally or flexibly coupled to each other at the commissures. Preferably, the stent comprises separate cloth-covered stent members that each define a cusp region and two commissure regions, adjacent commissure regions of the stent members together defining each of the commissures of the stent. The commissure regions of the separate stent members desirably remain spaced apart, with the leaflets extending therethrough to be attached between the cloth covering and the outer connecting band. In this manner, the leaflets are connected to separate stent members, and not to each other to facilitate flexing of the valve.
In another aspect of the present invention, a holder is provided for mounting the flexible heart valve. The holder includes a central hub with a plurality of radially outward upper legs, and a plurality of lower legs angled downward and outward. The upper and lower legs are adapted to connect to the alternating cusps and commissures of a flexible valve so as to maintain the position of the valve during implantation.
The present invention further provides a combination of a flexible prosthetic heart valve and a rigid holder. The flexible heart valve includes alternating cusps and commissures in a generally cylindrical configuration adapted to move radially in and out with respect to one another. The holder includes structure for maintaining a fixed shape of the flexible prosthetic heart valve during implantation.
In a still further aspect of the present invention, a heart valve leaflet is provided comprising a flexible, planar body having an arcuate cusp edge terminating at outer tips. The planar body includes a coapting edge that is defined by two relatively angled lines joined at an apex directed away from the cusp edge midway between the two tips. Desirably, the leaflet is made of pericardial tissue.
The present invention further provides a method of implantation of a heart valve, including the steps of: providing a flexible heart valve having alternating cusps and commissures in a generally cylindrical configuration and adapted to move radially in out with respect to one another; attaching a holder to the valve that restricts relative movement of the cusps and commissures; positioning the heart valve in proximity to an anatomical orifice; implanting the heart valve; and, disconnecting the holder from heart valve.